Srinivasan Subashini, Ennis Daniel B
Department of Bioengineering, University of California, Los Angeles, California, USA; Department of Radiological Sciences, University of California, Los Angeles, California, USA.
Magn Reson Med. 2014 Mar;71(3):1035-43. doi: 10.1002/mrm.24764.
Cardiac cine balanced steady-state free precession (bSSFP) imaging uses a high flip angle (FA) to obtain high blood-myocardium signal-to-noise and contrast-to-noise ratios (CNR). Use of high FAs, however, results in substantially increased SAR. Our objective was to develop a variable FA bSSFP cardiac cine imaging technique with: (1) low SAR and blood-myocardium CNR similar to conventional constant FA bSSFP (CFA-bSSFP) or (2) increased blood-myocardium CNR compared to CFA-bSSFP with similar SAR.
Variable FA bSSFP cardiac cine imaging was achieved using an asynchronous k-space acquisition, which is asynchronous to the cardiac cycle (aVFA-bSSFP). Bloch simulations and phantom experiments were performed to compare the signal, resolution, and frequency response of the variable FA bSSFP and CFA-bSSFP schemes. Ten volunteers were imaged with different aVFA-bSSFP and asynchronous CFA-bSSFP schemes and compared to conventional segmented CFA-bSSFP.
The SAR of aVFA-bSSFP is significantly decreased by 36% compared to asynchronous CFA-bSSFP (1.9 ± 0.2 vs. 3.0 ± 0.2 W/kg, P < 10(-10)) for similar blood-myocardium CNR (34 ± 6 vs. 35 ± 9, P = 0.5). Alternately, the CNR of the aVFA-bSSFP is improved by 28% compared to asynchronous CFA-bSSFP (49 ± 9 vs. 38 ± 8, P < 10(-4)) with similar SAR (3.2 ± 0.5 vs. 3.3 ± 0.5 W/kg, P = 0.6).
aVFA-bSSFP can be used for lower SAR or higher contrast cardiac cine imaging compared to the conventional segmented CFA-bSSFP imaging.
心脏电影平衡稳态自由进动（bSSFP）成像使用高翻转角（FA）来获得高的血液-心肌信噪比和对比噪声比（CNR）。然而，使用高翻转角会导致比吸收率（SAR）大幅增加。我们的目标是开发一种可变翻转角bSSFP心脏电影成像技术，该技术具有：（1）低SAR且血液-心肌CNR与传统的恒定翻转角bSSFP（CFA-bSSFP）相似；或（2）与CFA-bSSFP相比，在相似SAR的情况下血液-心肌CNR增加。
使用与心动周期异步的k空间采集实现可变翻转角bSSFP心脏电影成像（aVFA-bSSFP）。进行了Bloch模拟和模型实验，以比较可变翻转角bSSFP和CFA-bSSFP方案的信号、分辨率和频率响应。对10名志愿者使用不同的aVFA-bSSFP和异步CFA-bSSFP方案进行成像，并与传统的分段CFA-bSSFP进行比较。
对于相似的血液-心肌CNR（34±6 vs. 35±9，P = 0.5），aVFA-bSSFP的SAR与异步CFA-bSSFP相比显著降低了36%（1.9±0.2 vs. 3.0±0.2 W/kg，P < 10^(-10)）。或者，在相似SAR的情况下（3.2±0.5 vs. 3.3±0.5 W/kg，P = 0.6），aVFA-bSSFP的CNR比异步CFA-bSSFP提高了28%（49±9 vs. 38±8，P < 10^(-4)）。
与传统的分段CFA-bSSFP成像相比，aVFA-bSSFP可用于更低SAR或更高对比度的心脏电影成像。
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